Thrush: That Black, Smelly, Gooey Stuff

Keep your horse's feet clean and dry to help prevent issues like thrush from developing.

Photo: iStock

In the early 2000s I was privileged to present at the Bluegrass Laminitis Symposium, held in Louisville, Kentucky, and sponsor a trip to the conference for a couple young farriers who had been spending time at my clinic. Let’s just say these guys didn’t get to town much. One evening, after a day’s worth of symposium presentations, a group of us went to a nice steakhouse. When it came time for dessert, I suggested to one of my farrier friends that he try the crème brûlée.

“What is it?” he asked.

“You’ll see,” I said. The dessert arrived, he sampled it, and then proclaimed, “Well that ain’t nothing but vanilla pudding with crunchy stuff on top. But it’s good!”

That story is one of my all-time favorites, and it came to mind as I began to write about thrush. What is it? It’s the black, stinky gooey stuff in the bottom of your horse’s foot. I bet 90% or more of the feet I pick up have some black, smelly gooey stuff in them. And I probably get almost that high of a percentage of questions/comments from owners about their horses having “problems” with thrush.

Thrush is an anaerobic (able to survive with little to no oxygen) bacterial disease affecting the frog area and surrounding sensitive tissues of the horse’s foot. I don’t typically become involved in a case of thrush until it has invaded beneath the cornified (hardened) layers of the foot, is macerating the frog, causing pain, or invading damaged laminae in the bars of the foot to create an abscess. That doesn’t mean, however, that owners shouldn’t be proactive if they see and smell the black gunk in or beneath their horses’ frog area, around the bars of the foot, or in the space of the sole-wall junction (white line). Use a wire brush, a hydrogen peroxide (over-the-counter strength) flush, and a drying agent such as copper sulfate to remedy the issue.

Many people believe wet and unsanitary conditions are to blame for thrush; however, I’ve seen severe cases develop in pastured horses during one of our Texas summer droughts. They were living in desertlike conditions and eating round bales of coastal hay. On the other hand, during shoeing changes in horses wearing sole support, I frequently see very damp feet, yet very healthy frogs and soles. Thus, I believe the main causative agent to be—more precisely—urine-soaked decaying organic debris.

The best treatment for thrush is one that is individualized to your situation. Simply cleaning the foot as described and applying a daily over-the-counter astringent remedies most mild and early cases. Applying copper sulfate to the sulcus of the frog (the grooves adjacent to and in the middle of the frog) weekly might help prevent bigger problems. In the more advanced, painful cases in which bacteria has invaded the foot to the point that merely brushing away the debris elicits bleeding, I prefer to apply a compounded topical concoctionunder bandages for 7-10 days. I have even used carbon dioxide laser therapy to debride and sterilize the affected surface with positive results. Another common treatment is applying iodine or iodine-soaked cotton swabs to the foot. However, because iodine is inactivated as a disinfectant in the presence of organic debris, I don’t recommend it for hoof problems without thorough cleaning and bandage protection.

Bottom line: Your horse’s feet have a tough life, and black, stinky stuff will likely appear in them at some point. Keep his feet clean and dry, and don’t apply any treatments that don’t have proven track records. Foot damage caused by thrush, canker, abscesses, and foreign bodies can appear similar, so if you see blood or lameness, or if the problem persists more than three to four days, call your veterinarian.

About the Author

Bruce Lyle, DVM, has a diverse equine patient load with an emphasis the past 13 years on disease of the feet and the foot's biomechanical influence on other lameness and performance issues. He is also an author, presenter and inventor. He established the Aubrey Equine Clinic in Aubrey, Texas, in 1994 and can be reached at 940/440-3006.

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